With the rapid development of diode-pumped solid-state lasers during the past few years, a number of approaches have been adopted with the aim of optimizing the overall efficiency of such devices. In small, diode-pumped systems, high optical to optical conversion is most easily achieved with longitudinal/end-pumping configurations, and the potential scalability of this technique has been demonstrated convincingly with the tightly folded resonator (TFR) design. This particular configuration, which uses a slab geometry, is disclosed in U.S. Pat. No. 4,894,839 issued Jan. 16, 1990 in the name of T. Baer. Baer discloses a pumping scheme with a plurality of spaced apart laser diode pumping sources positioned along a lateral side of a block of laser material. An optical resonator incorporating the block is configured in a tightly folded zig-zag configuration with the aim of optimizing the degree of spatial overlap between the pumped laser material and the optical resonator mode.
The alternative to end pumping is side-pumping, where the direction of pumping is transverse or orthogonal to the longitudinal axis of the laser cavity. Continuous wave (CW) or quasi-CW diode bars have been used in this configuration with relatively high power systems, however this approach tends to be much less efficient than end-pumping and considerable care must be taken to ensure that there is a high degree of overlap between the laser mode and the pumped volume. A major source of inefficiency in most side-pumping schemes is that the pump light is absorbed preferentially near the surface while the laser mode is located in the interior of the active medium. Partial solutions to this problem are: the use of a low absorption material with a large mode volume; partial focusing of the pump light in order to increase the pump intensity at the location of the mode; or, to use a slab geometry which makes direct use of the gain at the air/material interface. This last approach has the advantage that gain and refractive index non-uniformities are averaged-out by the mode as it interacts with the pumped region of the laser material. It is an object of this invention to provide a side-pumping configuration which is less complex but comparable in efficiency to the TFR scheme of Baer. Contrary to Baer's method this invention includes a laser cavity configured to have a reflection within the laser material at a high angle of incidence with respect to the normal rather than a tightly folded zig-zag configuration.